The present disclosure relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device that can prevent motion blurring and improve brightness, and a driving method thereof.
The LCD device displays an image by controlling light transmittance of a liquid crystal (LC) layer using an electric field applied to the LC layer in response to a video signal. Since the LCD device is a flat display device having characteristics of a small size, a slim profile, and low power consumption, it is widely used for a portable computer such as notebook personal computers (PCs), office automation (OA) apparatuses, and audio/video apparatuses. The LCD device having the characteristics of a slim profile and low power consumption is rapidly replacing cathode ray tubes (CRTs).
Since the LCD device is driven in a hold type that uses the slow response characteristic of LCs and the maintain characteristic of the LCs, a motion blurring phenomenon that an image appears dim or a tailing phenomenon that the outline of an image is dragged while a moving image is realized. Such reduction in image quality of a moving image is difficult to completely remove even when the response time of the LCs is faster than 1 frame period of 16.7 ms.
Meanwhile, the CRT is an impulse type display device instantaneously displaying an image, not maintaining data. Accordingly, motion blurring or tailing is nearly not generated while a moving is realized in the CRT. In detail, referring to FIG. 1A, the CRT allows a phosphor body to emit light for a very short initial time of one frame period (≈0.16.7 ms) to display data, and does not allow the phosphor body to emit light for the rest of the frame period. The impulse characteristic of the CRT allows a user to clearly view a moving image displayed on the CRT.
Unlike the CRT, referring to FIG. 2, the LCD device maintains a data voltage supplied to an LC cell for one frame period. Due to this hold characteristic of the LCD device, a user feels motion blurring or tailing in a moving image. The hold characteristic of the LCD device reduces display quality of a moving image. A “scanning backlight” method is proposed to remove reduction in display quality of a moving image caused by the hold characteristics of the LCD device.
FIG. 2 is a view illustrating a related art LCD device driven in a scanning backlight method.
Referring to FIG. 2, a related art LCD device includes an LC panel 2 including a plurality of pixel regions defined by a plurality of gate lines GL1-GLn and a plurality of data lines DL1-DLm to display an image on the pixel regions, a gate driver 4 driving the plurality of gate lines GL1-GLn, a data driver 6 driving the plurality of data lines DL1-DLm, a timing controller 8 controlling the gate driver 4 and the data driver 6, a backlight unit 10 including a plurality of lamps illuminating light onto the LC panel 2, and a lamp driving unit 12 sequentially driving the plurality of lamps.
The lamp driving unit 12 sequentially lights on/off the plurality of lamps included in the backlight unit 10 using a lamp driving voltage supplied from a power generator (not shown) under control of the timing controller 8. In the case where the number of the lamps included in the backlight unit 10 illuminating light onto the LC panel 2 is sixteen, the plurality of lamps are lighted on when power is supplied from the lamp driving unit 12, and lighted off when power is not supplied from the lamp driving unit 12. The lamp driving unit 12 includes a scan signal generating part and an inverter to sequentially light on/off the plurality of lamps. The scan signal generating part receives a horizontal synchronization signal Hsync and a vertical synchronization signal Vsync from the timing controller 8 to generate a lamp on/off signal for sequentially lighting on/off the plurality of lamps, and supplies the lamp on/off signal to the inverter. The inverter supplies a lamp driving voltage to each lamp in response to the lamp on/off signal to sequentially light on/off the plurality of lamps for one frame, thereby driving the LCD device in a scanning backlight method.
The scanning backlight method lights on/off a plurality of lamps along a scanning direction. According to the scanning backlight method, an LCD device emits light for a predetermined time section of one frame period and blocks light for the rest of the one frame period as the plurality of lamps are sequentially lighted on/off along a scanning direction, thereby operating in a quasi-impulse type. Therefore, application of the scanning backlight method can improve display quality of a moving image in an LCD device.
In an LCD device driven using the scanning backlight method, the duty ratios of a plurality of lamps are set to 60% to enhance image quality of a moving image. The LCD device driven using the scanning backlight method gradually reduces the lighted-on times of the plurality of lamps to solve a limitation such as motion blurring, thereby enhancing image quality of a moving image. Since the display quality of a moving image in an LCD device is excellent at the duty ratio of 60% for the plurality of lamps, the LCD device applying the scanning backlight method generally applies a duty ratio of 60% to control the lighted on/off times of the plurality of lamps. When a duty ratio of 60% is applied to the plurality of lamps, brightness remarkably falls down compared to the backlight method always lighting on the lamps. Accordingly, when the scanning backlight method sequentially lighting on/off a plurality of lamps is applied to an LCD device to solve a limitation such as motion blurring, a limitation of brightness reduction is generated.